1. Field of the Invention
The present invention relates to a method and apparatus for the computerized mechanical palpation of the breast and detecting changes in mechanical properties of the breast tissue that are indicative of breast cancer and other breast pathologies accompanied by changes in the tissue viscoelasticity.
2. Description of the Related Art
Breast cancer is a major source of cancer morbidity and mortality in women. Various techniques have been developed for early diagnosis of breast cancer including ultrasonic imaging, nuclear magnetic resonance imaging, x-rays, and the like. Currently, the most widely used clinical method of diagnosing breast cancer is mammography. Efforts to reduce mortality via screening mammography have been successful with improvement in survival, particularly in women over 50 years old. One of the major disadvantages of the use of mammography is patients"" exposure to radiation.
One of the safest and oldest techniques of detecting tissue disease is manual palpation. Palpation encompasses examination using the sense of touch, and is based on the significant difference in elasticity of normal and diseased tissues. Overall, about two-thirds of cancers are detected by palpation. Such sensitivity is related to significant changes in mechanical properties of tissues in the course of breast cancer development. In the United States the technique of self-palpation is widely taught to women as an effective means of early cancer detection. A significant fraction of breast cancer is first detected by women themselves who find suspicious lesions within their breasts and bring the problem to the attention of their physicians. The main disadvantage of manual palpation is its high degree of subjectivity. The examiner has to instinctively relate what he or she perceives by the finger to his or her previous experience. Moreover, a physician performing the examination cannot objectively record the state of the examined breast.
A number of devices have been developed for detecting regions of hardening in the breast tissues. Several authors have proposed various devices for breast palpation using different types of force sensors, but all with limited success. For example, a device described by Gentle in Gentle CR, xe2x80x9cMammobarography: A Possible Method of Mass Breast Screeningxe2x80x9d, I. Biomed. Eng. 10, 124-126, 1988 was capable of detecting xe2x80x98lumps of 6 mm in diameter in breast phantoms but was unable to obtain any quantitative data on lumps in a human breast. Many of the proposed breast self examination means were related to simple non-computerized mechanical systems enhancing sense of touch such as apparatuses described in U.S. Pat. No. 5,572,995, U.S. Pat. No. 4,657,021, U.S. Pat. No. 4,793,354, and U.S. Pat. No. D348,618.
Various types of devices mimicking manual palpation for detecting breast tumors using different types of force sensors have been developed. For example, Frei et al., U.S. Pat. No. 4,250,894, describes an instrument which uses a number of piezoelectric strips pressed into the breast during the examination by a pressurizing unit which applies a given periodic or steadyxe2x80x99 stress to the tissue beneath the strips.
Another method and device for breast examination are described in the U.S. Pat. No. 5,883,634 and U.S. Pat. No. 5,989,199. The sensors used in this device are based on the force sensor array manufactured by Tekscan Inc., Boston, Mass. The array consists of conductive rows and columns whose intersecting points form sensing locations. A material, which changes its electrical resistance under applied force, separates the rows and columns. Thus, each intersection becomes a force sensor. Clinical data obtained using this device were published in February 1999 issue of the Oncology News International, in an article entitled xe2x80x9cElectronic Palpation May Detect Breast Cancersxe2x80x9d. The device showed an overall sensitivity of 92% (detecting 108 of 118 palpable and nonpalpable lesions) vs. 86% for the physician""s exams (102 of 118 lesions). The device correctly detected all eight palpable cancers found in the study population and two of three non-palpable cancers.
Conventional imaging modalities capable of detecting motion of a tissue subjected to an external force (such as ultrasound or MRI) use indirect means of evaluation for determining the elasticity of the tissues. One such approach is based on determining the relative stiffness or elasticity of the tissue by applying ultrasound imaging techniques while vibrating the tissue at low frequencies. See. e.g., K. I. Parker et al, U.S. Pat. No. 5,099,848; R. M. Lerner et al., Sono-Elasticity: Medical Elasticity Images Derived From Ultrasound Signals in Mechanically Vibrated Targets. Acoustical Imaging, Vol. 16, 317 (1988); T. A. Krouskop et al., A Pulsed Doppler Ultrasonic 241, Rehab. Res. Dev. Vol. 24, 1 (1987); and Y. Yamakoshi et al., Ultrasonic Imaging of Internal Vibration of Soft Tissue Under Forced Vibration, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 7, No. 2, Page 45 (1990).
Another method proposed for measuring and imaging tissue elasticity is described in Ophir et al., U.S. Pat. Nos. 5,107,837, 5,293,870, 5,143,070 and 5,178,147. This method includes emitting ultrasonic waves into the tissue and detecting an echo sequence resulting from the ultrasonic wave pulse. The tissue is then compressed (or alternatively decompressed from a compressed state) along the path. During such compression a second pulse of ultrasonic waves is sent along the path into the tissue. The second echo sequence resulting from the second ultrasonic wave pulse is detected. Next, the differential displacement of the selected echo segments of the first and second echo sequences are measured. A selected echo segment of the echo sequence, i.e., reflected RF signal, corresponds to a particular echo source within the tissue along the beam axis of the transducer. Time shifts in the echo segment are examined to measure compressibility of various regions in the examined tissue.
All presently available methods of palpatory assessment of the breast are inferior to manual palpation in sensitivity and specificity. Therefore, further development of screening techniques with greater sensitivity, specificity and accuracy is urgently warranted. It is desirable to provide computerized palpation of the breast which is capable of detecting breast lesions with sensitivity and spatial resolution exceeding that of manual palpation for use in early diagnostics of breast cancer.
The invention will be more fully described by reference to the following drawings.
The present invention provides a device and method for detection of abnormalities in tissues accompanied by the changes in their elasticity (such as those caused by cancer). The method is based on a computerized mechanical imaging referred to herein as CMI. The essence of CMI is the reconstruction of the internal structure of the soft tissues in a human body by measuring a dynamic or oscillatory stress pattern using an array of pressure sensors. The pattern of the dynamic mechanical stress and its changes as a function of applied pressure and time contain comprehensive information on the mechanical properties and geometry of the internal structures of the studied tissues.
The CMI devices are applicable in those fields of medicine where palpation is proven to be a sensitive tool in detecting and monitoring diseases (including but not limited to the breast cancer.
In a preferred embodiment, the apparatus for mechanical imaging of the breast comprises an electronically controlled mechanical scanning unit with a number of pressure transducers and an electronic unit for data acquisition, processing and displaying of images. The mechanical scanning unit includes a compression mechanism, three-dimensional positioning system, and local pressure source with a linear pressure sensor array opposing a two-dimensional pressure sensor array. The local pressure source is either a roller that is moved over the examined breast or, in an alternate embodiment, a linear pressure sensor array which can be moved in three dimensions. The electronic unit receives the pressure data from the pressure transducers and the position data from the positioning system and determines the mechanical structure of the breast.
The apparatus of the current invention uses sensors based on piezoelectric films, such as piezopolymer polyvinylidene fluoride (PVDF) and comprises mechanical arrangements allowing increasing PVDF signal. The piezopolymer film provides inexpensive means for measuring mechanical forces by converting them into electrical signals.
In the method of the present invention, the position data and pressure response data are acquired for translational and oscillation displacement overlaying the breast by periodic pressing or oscillating the linear pressure sensor array attached to the slider pressed against the breast. A pattern of pressure responses, pressure gradient responses, and spectral characteristic of pressure responses are determined and used for generating a mechanical image of the breast.
The present invention utilizes the similar mechanical information as obtained by manual palpation conducted by a skilled physician but objectively and with higher sensitivity and accuracy. The essence of the proposed method and device is detection of tissue heterogeneity by measuring changes in the surface stress pattern using a force sensing array applied to the tissue in the oscillatory mode. Temporal and spatial changes of the spectral components and phase relationships of oscillatory signals from the sensors contain information on the mechanical properties and geometry of the internal structures of the breast. The device and method in accordance with the present invention enable the user to detect changes in the breast tissue that are indicative of cancer development.
The present invention expands on teachings of inter-relation of mechanical heterogeneities in the tissue and respective changes in the measured stress patterns, and temporal and spatial derivatives of the oscillatory signals from the force sensors on the surface of the tissue. The present invention also expands on the teaching that the above relationship forms the basis for a method of detecting and quantifying tissue abnormalities.
With the foregoing and other objects, advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by referencing to the following detailed description of the invention, the appended claims and the several views illustrated in the drawing.